Enteral nutrition is generally preferred over parenteral nutrition because of its lower cost, lower rate of complications, and effective preservation of gut structure and function. Many critically ill patients cannot tolerate naso-gastric tube feeding, developing manifestations of intolerance including nausea, vomiting, and abdominal distension and aspiration. Gastric residual volumes are widely used to evaluate feeding tolerance and gastric emptying. High gastric residual volumes raise concern about intolerance to gastric feeding and the potential risk for regurgitation and aspiration pneumonia. Furthermore, high gastric residual volumes may be one of the key contributing factors to intra-abdominal hypertension. Values of gastric residual volumes cited as being high in patients receiving naso-gastric feeding typically range from 75 to 500 ml.
Conventional use of gastric residual volume measurement obtained by aspiration via a syringe is a time consuming procedure. The size of standard syringes for this purpose is limited to 100 ml, which means that a residual volume of e.g. 300 ml will require three aspiration cycles. The aspirated volume must be stored temporarily in a container because a residual volume lower than a critical volume should be returned to the patient's stomach, using the syringe for the re-injection of the aspirated volume. If the total aspirated volume is higher than the critical volume, it will be discarded in its entity. The critical volume varies from hospital to hospital, but is typically 100-499 ml. The procedure of aspirating a patient's stomach will often be delayed because the naso-gastric tube may collapse in response to the negative pressure created when aspirating with the syringe.